1. Field of the Invention
The present invention relates to a sensor and an assembly method, and more particularly, to a stress sensor fixing to an electronic device and an assembly method thereof.
2. Description of the Related Art
The stress sensor adapted to be used as pointing device is widely used in many types of electronic devices such as laptop, mouse device, keyboard, hand-held device, joystick and the like. For example, the common stress sensor of a laptop is arranged among keys of the keyboard. When a user touches the stress sensor with a finger, the stress sensor senses the magnitude and the direction of the force exerted by the user and then a corresponding movement of cursor is performed.
FIGS. 1A and 1B are schematic three dimensional and exploded views of a conventional stress sensor respectively. A conventional stress sensor 10 includes a metallic back plate 11, a circuit board 12, a pointing stick 13, a fixing element 15 with a hollow portion 151 for penetrating the pointing operation element 13 through, fastening holes 161, screws 162 in accordance with the fastening holes 161, an insulating plate 17 interposed between the back plate 11 and the circuit board 12, an insulating plate 18 interposed between the circuit board 12 and the fixing element 15 and a stress sensitive structure including a stress deformation region and resistors (not shown).
FIG. 2 schematically illustrates a bottom surface of a circuit board used in conventional stress sensor. As shown in FIGS. 1A, 1B and 2, the pointing stick 13 and the resistors 14 are disposed on a top 121 and a bottom 122 of the circuit board 12 respectively. The resistors 14 include the resistors 141 and 142 for sensing horizontal forces and the resistors 143 and 144 for sensing vertical forces. When the pointing stick 13 is pushed in a desired direction by a finger of the user, a part of the circuit board (i.e. the stress deformation region 123) connected to the bottom of the pointing stick 13 is deformed and thus the resistance values of the stress sensitive resistors 14 is changed. Accordingly, a resistance change is detected by a microprocessor or a controller (not shown) connected to the stress sensor 10, and corresponding movement of the cursor on the display screen is rendered.
Therefore, when the conventional stress sensor is attached onto a structure such as keyboard body of an electronic device by fastening screws through the fastening holes 163 of the fixing element 15, the overall height and the overall weight of the electronic device are increased and thus the electronic device can not achieve advantages of small in size and light weight. In addition, the larger amounts of the elements of the conventional stress sensor reduce the assembly efficiency and increase the cost.